The present invention relates to hole drilling devices and, more particularly to hole saws, which, for example, include a cylindrical saw blade, one end of which is provided with a circumferential row of saw teeth, while the opposite end is associated with a carrier plate having a central hole for receiving a drill bit and a collar portion adapted to be clamped to the drill bit so as to enable the hole saw member to be fixed to the drill bit and rotate therewith when the drill bit is caused rotated when, for example, mounted in the chuck of a drilling machine. Hereby the drill bit as protruding from the plane of the free annular saw tooth edge of the hole saw implement provides for an initial centering of the cylindrical hole saw element, which will thereafter cut out a corresponding hole in the material member in question in response to axial displacement of the combined drill bit and circular hole saw element, such that a hole may be drilled or rather sawed, the diameter of which exceeds the maximum diameter of drill bits as mountable directly in the chuck of the drilling machine.
Hole drilling implements of the aforementioned type have been proposed which generally include a carrier member, with the carrier plate and collar portion being formed in one piece, and the cylindrical saw blade being secured to the carrier plate, while the collar portion is provided with a radial clamp screw for fastening the implement to the shank of a drill bit in a desired axial position on the bit. It is well known, however, that a safe fastening of the implement for preventing mutual rotation of the drill bit and the implement requires a high pressure of the clamp screw against the bit shank surface, whereby the collar portion must be of a heavy construction, or the clamp screw cooperates with a recess or flat face portion of the bit shank, whereby the drill bit has to be specifically designed for the specific purpose.
It is the object of the invention to provide hole drilling device of the aforementioned type, which is of a simple design and yet easily fastenable to the drill bit.
According to the invention the collar portion of the carrier plate includes an axially split sleeve member of a cylindrical configuration operable to receive a selected standard drill bit with loose fit and to be inserted, together with the drill bit, into a clamping chuck so as to be fastenable to the drill bit and to the chuck by actuation of the radial clamp means of the chuck. Thus, the drill bit need no adaption whatsoever, and the collar portion of the implement will be firmly secured by the tightening of the chuck.
Under these conditions the collar or sleeve portion does not require any clamp screw, and it may be made of a relatively thin metal sheet material. This leads to a further and important development according to the invention, namely that the entire implement may be made from a sheet blank, which is pressed into a shape comprising both the saw blade cylinder, the carrier plate portion and the sleeve portion, whereby the implement may be produced at very low costs.